Q: Static ip address issue

You'll need to tell us a bit about your network.

How exactly is your network set up?

Do you have a DHCP server running on this network handing out other IP addresses?

What is providing internet access to the network?

How are the Airports setup? As Wifi extenders?  Routers? 

Have you checked whatever is acting as your main router to see if it has blocked the 40 IP address for any reason?

Do you get an error when assigning the 40 IP address? Like "already in use" or something similar?

When using a fixed IP address, you often have to provide your own DNS server address as well.

System Preferences -> Network -> Advanced -> DNS -> [+]

OpenDNS.org

208.67.222.222

208.67.220.220

Google DNS

8.8.8.8

8.8.4.4

Are good public DNS servers.

Try using a utility such as

WakeOnLan

<http://www.readpixel.com/wakeonlan/index.html>

which will display every IP address visible.  That should help you identify if there is a conflicting x.y.z.40 address.

Or Bonjour Browser

<http://www.tildesoft.com>

Or

Flame

<http://husk.org/apps/flame/>

Which will identify systems on the network based on Bonjour advertisements.

Stupid question. You are sure that the x.y.z part of x.y.z.40 is the same as the router's x.y.z.  That is to say, there is no typo.

Another approach is to configure your router to have reserved IP addresses for all your devices.  Then the devices use DHCP, but the router always gives them the same IP address.  This is more flexible, as when you leave the house with one of the devices, it can get a DHCP address when using another WiFi access point, but always get the same fixed IP address at home.  Most routers offer this service.  They either bind to the xx:xx:xx:xx:xx:xx MAC address or some can bind to the System Preferences -> Network -> Advanced -> TCP/IP -> DHCP Client ID.  Having the router assign the IP address also means the router will provide DNS server information as well.

Server rookie wrote:

 

Thanks Phil0124. The network is pretty simple. It's vdsl router (takes care of the dhcp) to airport to switch. All devices and other airports are connected to the switch. All Cat6 shielded. The airports act as wifi extenders. I don't get a warning that I can't use the ip address that end on 40, it just doesn't connect to the internet. The wifi and ethernet setup of a device can have the same address as there're not used at the same time, can't they?

Depends.

If both the ethernet and the wifi are connecting to the same network then you should be getting an "already in use"  or "There is an IP address conflict with another system on the network" error and you will have issues.

If they are connected to different networks that just happen to use the same IP address range, then there should be no problems there.

In other words each interface is its own connection on a network and would need a different IP address if connected to the same network.

If you gave both interfaces the 40 IP address, then your problem lies there.

Give one of them a different IP address. 

I have given the same IP address to WiFi and Ethernet on the same Mac and it works rather nicely.  It is possible this works because OS X makes just one interface the primary interface, and the other interface steps away.  So the rest of the LAN does not see two of the same IP address at the same time.

The nice thing about giving the WiFi and Ethernet the same IP address is that  if you have any network connection going, such as a file transfer, you can plug in an ethernet cable and the transfer will start using the faster ethernet, then unplug the ethernet, and it will go back to the WiFi.  The network connection will stay up the entire time.

However, when the network is not working, you can try changing the IP address on the interface you do not want to be using at the moment, and see if that changes anything.